1. Field of the Invention
The present invention relates to capacity optimization in communication channels. More particularly, the present invention relates to optimization of Reverse Outer Loop Power Control (ROLPC) when the channel is capable of discontinuous transmission (DTX).
2. Description of the Related Technology
Wireless communication systems are widely deployed to provide various types of communication such as voice, data, and so on. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), or some other modulation techniques. A CDMA system provides certain advantages over other types of systems, including increased system capacity.
A CDMA system may be designed to support one or more CDMA standards such as (1) the “TIA/EIA-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (the IS-95 standard), (2) the standard offered by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), (3) the standard offered by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in a set of documents including “C.S0002-A Physical Layer Standard for cdma2000 Spread Spectrum Systems,” the “C.S0005-A Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems,” and the “C.S0024 cdma2000 High Rate Packet Data Air Interface Specification” (the cdma2000 standard), and (4) some other standards.
Resource limitations drive a constant demand for increased channel capacity in communication links. The resource limitations may include space limitations, such as the internal dimensions of a conduit for wire-line communication channels, temporal limitations, such as allowable delay in real time data analysis, or bandwidth limitations, such as frequency spectra in wireless transmission channels where the spectral bandwidth of a channel is regulated.
Various techniques have been developed and implemented in order to increase channel capacity. Communication channel capacity may be increased by implementing multiplexing techniques, examples of which include, but are not limited to, time multiplexing, frequency multiplexing, code multiplexing, or a combination of multiplexing techniques.
Many users share a single communication channel when the channel is multiplexed. A user allocated a portion of the multiplexed channel may engage in active, continuous transmission over the allocated channel or may engage in discontinuous transmission (DTX) where transmission on the allocated portion of the channel is not continuous but may be burst transmissions.
Closed loop power control is used in the reverse link of a CDMA wireless communication system to ensure the reverse link transmit power is accurately controlled. In reverse closed loop power control, a base station (BS) (or base station controller (BSC) measures the signal level received from each mobile station (MS) and provides feedback to each MS with instructions to adjust the MS transmit power. The closed loop power control loop attempts to adjust each MS transmit power to cause the reverse link transmit signals from all of the MS in the cell to arrive at the minimum level of power required for each MS to achieve a desired Quality of Service (QoS).
The base station measures the received signal-to-interference (Eb/I0) and compares the measured value to an adjustable threshold known as the power control setpoint. When the measured Eb/I0 is above the setpoint, the base station instructs the MS to reduce the reverse link transmit power by a predetermined amount, e.g., 1 dB. When the measured Eb/I0 is below the threshold, the BS sends the MS a command to increase the reverse link transmit power by a fixed amount.
The value of the power control setpoint largely determines the QoS maintained by the MS. The QoS is measured as a Frame Erasure Rate (FER), alternatively known as the Frame Error Rate. As expected, increasing the value of the power control setpoint reduces the FER, thereby providing a higher QoS. Reducing the power control setpoint increases the FER. Adjusting the threshold of the power control setpoint occurs in a process known as Reverse Outer Loop Power Control (ROLPC).
The implementation of ROLPC for just one active channel (e.g., in a CDMA 2000 system operating in P1 mode) is relatively straightforward because frames are continuously transmitted on the active channel by the MS and the Eb/I0 and FER may be updated based on the active channel. However, when multiple channels are active and discontinuous transmission (DTX) is allowed for one or more channels, the implementation is substantially more complex. One difficulty is accurately distinguishing between frames that are DTX and frames that are not DTX but contain one or more bit errors after decoding.
Imperfect determinations of DTX and non-DTX frames result in a power control setpoint threshold that is imperfect. A setpoint that is too high results in reduced channel capacity.
It is desirable, during ROLPC adjustment of the power control setpoint to compensate for inaccurate DTX and non-DTX indications to optimize the power control setpoint and thus the reverse channel capacity.